Ecological studies on birds tend to be biased towards the breeding season, yet understanding the full annual cycle of an organism is critical for understanding how effects carry over between the seasons. The aim of this thesis is to gain a more complete picture of Herring Gull movements outside the breeding season. By examining the migration and wintering patterns of Herring Gulls from five different sites across their breeding range in eastern North America, I evaluate the variability in the behaviour of this highly flexible species, both among individuals and populations. My research reveals for the first time that Herring Gulls breeding in the Arctic migrate long distances to spend the winter in the Gulf of Mexico. I confirm that Herring Gulls from the Great Lakes disperse and do not truly migrate. Regardless of the distance they travelled, Herring Gulls tended to migrate at a seemingly relaxed pace, with many stopovers and indirect routes. Each population of Herring Gulls had strong migratory connectivity between their breeding and wintering are as, meaning that environmental stressors in one area can potentially have strong population-specific effects. This finding gives a particular significance to the differences I observed in winter habitat use among populations. I found that Herring Gulls from the Arctic spent the majority of the winter in marine habitats, while those from the Great Lakes and Atlantic Canada used a wider variety of habitats. However, only in the Atlantic populations did a large proportion of individuals spend most of their time in urban habitats. Previous studies have found that Herring Gulls in Atlantic Canada have lower survival rates than those in the Great Lakes and the Arctic, which suggests that there may be a link between urban habitat use during the winter and poor adult survival.

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